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`TOPICS IN LIGHTWAVE
`
`MEMS Optical Switches
`
`Tze-Wei Yeow, K. L. Eddie Law, and Andrew Goldenberg, University of Tor onto
`
`ABSTRACT
`
`Leveraging MEMS's inherent advantages
`such as batch fabrication technique, small size,
`integratability, and scalability, MEMS is posi(cid:173)
`tioned to become the dominant technology in
`optical crossconnect switches. MEMS optical
`switches with complex movable 3D mechanical
`structures, micro-actuators, and micro-optics can
`be monolithically integrated on the same sub(cid:173)
`strate by using the matured fabrication process
`of the integrated circuit industry. In this article
`we report various popular actuating mechanisms
`and switch architectures of MEMS optical
`switches. The basics of surface and bulk micro(cid:173)
`machining techniques used to fabricate MEMS
`devices will be reviewed. Examples of 2D and
`3D approaches to MEMS optical switches wi ll
`be described. The pros and cons of the two
`approaches will be analyzed. In the short term,
`MEMS-based optical switches seem to have cap(cid:173)
`tivated the attention of both the industry and
`academia. H owever, there are challenges that
`threaten the long-term survival of this technolo·
`gy. The problems that remain to be fully
`addressed will be discussed.
`
`INTRODUCTION
`One of the most promising applications of micro(cid:173)
`electromechanical systems (MEMS) technology
`is in optical communication in general and opti(cid:173)
`cal crossconnect (OXC) switches in particular.
`T he OXC switches in today's network rely on
`electronic cores. As port count and data rates
`increase, it becomes increasingly difficult Cor the
`electronic switch fabrics to meet future demands.
`I ris widely acknowledged that electronic switch
`fabrics are the bottleneck in tomorrow's commu(cid:173)
`nication networks. This bottleneck has stimulat(cid:173)
`ed intensive research in developing new
`all-optical switching technologies to replace the
`electronic cores. All-optical networks offer many
`advantages compared to conventional optical-to(cid:173)
`electronic and electronic-to-optical networks,
`including cost-effectiveness, immunity from elec(cid:173)
`tromagnetic interference, bit rate/protocol trans(cid:173)
`parency,
`and
`ability
`to
`implement
`wavelength-division multiplexing (WDM) with
`relative ease. Therefore, it is desirable to manip(cid:173)
`ulate the data network at the optical level with
`
`optical switches. The optic switches are used to
`reconfigure/restore the network, increase irs relia(cid:173)
`bility, and/or act as the optical add/drop multi·
`plexer (OADM). There are, indeed, many
`technologies competing to replace the current
`electronic switch fabrics. A successful optical
`switching technology will have to demonstrate
`superiority in the areas of scalability, insertion
`loss, polarization-dependent loss (PDL), wave(cid:173)
`length dependency, small size, low cost, crosstalk,
`switching speed, manufacturability, serviceability,
`and long-term reliability. Conventional mechani·
`call-witches, which are based on macroscopic bulk
`optics, utilize the advantages of free-space optics;
`however, they suffer from large size, large mass,
`and slow switching time. On the other hand, guid(cid:173)
`ed-wave solid state switches have yet to show
`great potential because their high losses and high
`crosstalk limit their scalability. The recent devel(cid:173)
`opment of free-space optical MEMS technology
`has shown superior performance for this applica(cid:173)
`tion. MEMS optical switches not only retained
`their conventional counterparts' advantages of
`free-space optics such as low losses and low
`crosstalk, but also included additional ones such
`as small size, small mass, and submillisecond
`switching times. Furthermore, MEMS fabrication
`techniques allow integration of micro-optics,
`micro-actuators, complex micromechanical struc(cid:173)
`tures, and possibly mkroelectronics on the same
`substrate to reali.ze integrated microsystems.
`
`MICROMACHINING TECHNIQUES
`MEMS fabrication techniques utilize the mature
`fabrication technology of the Integrated Circuit
`(IC) industry. The fact that silicon is the primary
`substrate material used in the IC circuitry and
`that it also exhibits excellent mechanical proper(cid:173)
`ties [1) make it the most popular micromachin(cid:173)
`ing material. The micro-mechanical structures
`used in MEMS optical switching can be fabricat(cid:173)
`ed using two popular micromachining technolo(cid:173)
`gies, bu lk micromachining, and surface
`micromachining.
`
`BULK MICROMACHINING
`This is the most mature and simple microma(cid:173)
`chining technology. Bulk micromachin ing is
`sometimes called the etching/subt raction pro(cid:173)
`cess. It involves the removal of silicon from the
`
`158
`
`0163-6804/01/$10.00 © 2001 IEEE
`
`IEEE Communications Magazine • November 2001
`Capella 2007
`Ciena/Coriant/Fujitsu v. Capella
`IPR2015-00816
`
`
`
`
`
`

`

`(1 00) Surface orientation
`
`Silicon substrate
`
`(1 00) Surface orientation
`
`Silicon substrate
`
`(a)
`
`(100)
`Surface orientation
`
`Anisotropically
`etched cavity
`9 = 54.74°
`
`< 111 >Surface
`orientation
`
`(b)
`
`Silicon substrate
`
`(c)
`
`• Figure 1. a) Anisotropic wet etching of (100) and (110) silicon substrate; b)
`deep cavity fomz in silicon by anisotropic etchants; c) isotropic etching of silicon.
`
`Structural layer
`~ ?????>t .,, s;p; 6;
`
`Sacrificial layer
`I
`
`•
`
`L
`
`F
`
`bulk silicon substrate by etchants. There are two
`ty pes of chemical e tchants, anisotropic a nd
`isotropic. Anisotropic etchants etch different sili(cid:173)
`con orientation planes at different rates. Figure
`1 a shows the silicon planes exposed by using
`anisotropic etchants. Figu re lb shows a 30
`mechanical structure that was fabricated using
`anisotropic etching.
`Isotropic etchants, on the o ther hand, e tch
`the silicon evenly in all directions. Figure 1c
`shows the e ffect of isotropic etches on silicon
`substrate. Note that the mechanical structure
`that can be created by bulk micromachiniog is
`not very complex.
`
`SURFACE MICROMACHINING
`Surface micromachining is a more advanced
`fabrication technique. Complex 30 mechanical
`structures ca n be created using alternate layers
`of sacrificial and structural materials. Sacrificial
`laye rs act as spacers between structural layers.
`Free-standing 30 mechanical structures will be
`form ed whe n the sacrificial layers arc etched
`away during final release. Tn surface microma(cid:173)
`chining, thin-film materials are selectively added
`to or removed from the wafer. Thin-film materi(cid:173)
`al deposited where a free-standing mechanical
`structure is needed is called a sacrificial layer.
`The material that is left after etching of the
`underlying sacrificial layer is called the s truc(cid:173)
`tural material. In surface micromachining, a
`combination of dry and wet etching, and thin(cid:173)
`film deposition are essential processes to realize
`micromechanical structures on silicon. A sacrifi(cid:173)
`cial layer, such as silicon dioxide, are deposited
`or grown underneath a patterned material for
`later removal. The removal process is usually
`done by chemical etching. After the removal of
`the sacrificial layer, the patterned material is
`left as thin-film free-standing mechanical struc(cid:173)
`tures as t hey are suspended over the substrate
`by the thickness o f the e tched sacrificial layer.
`Figure 2 shows the surface micromachining pro(cid:173)
`cess o f creating a free-standing mechanical
`structure. An insulation layer has been deposit(cid:173)
`ed on the silicon substrate, followed by deposi(cid:173)
`tion of Si02 as the sacrifi cial layer. The
`structural layer is the n deposi ted on the Si02.
`Openings are etched in the s tructural layer to
`expose the sacrificial layer. The underlying sac(cid:173)
`rificial layer is etched away to release the free(cid:173)
`standing structural layer.
`
`SWITCH A RCHITECTURES
`There arc currently two popular approaches to
`implement MEMS optical switches:
`• 20 MEMS switches
`• 30 MEMS switches
`These two technologies have striking differences
`in terms of how they are controlled and their
`ability to redirect light beams. However, both of
`them have shown promise in fi nding their niches
`in telecommunication networks.
`
`20 MEMS SW ITCHES
`In this architectu re mirrors arc arranged in a
`crossbar configuration as shown in Fig. 3. Each
`mirro r has o nly two positions and is placed at
`the intersections of light paths between the input
`
`• Figure 2. Swface micromachining process
`where the sacrificial layer is first deposited or
`grown for later removal. In the process, free(cid:173)
`standing mechanical structures are released.
`
`JEEE Communications Magar.ine • November 2001
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`159
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`

`

`Most distance path
`
`/
`
`/
`
`ON
`
`OFF
`
`Outputs
`
`Inputs
`
`least distance path
`
`• Figure 3 . A 2D crossbar switching architecture.
`
`• Figure 4. A closeup view of a WaveStar'" MEMS
`mirror [2}.
`
`and output ports. They can be in either the ON
`position to reflect light or the OFF position to
`let light pass uninterrupted. The binary nature of
`the mirror positions greatly si111plifies the control
`scheme. Typically, the control circuitry consists
`of simple transistor-transistor-logic (ITL) gates
`and appropriate amplifiers to provide adequate
`voltage levels to actuate mirrors.
`For anN x N-port switch, a total of N2 mir(cid:173)
`rors is required to implement a strictly non(cid:173)
`blocking optical switching fabric. For example, a
`16 x 16-port switch will require 256 mirrors. An
`alternative approach to increasing port count is
`to interconnect smaller 2D MEMS switch sub(cid:173)
`modules to form multistage network architecture
`such as the well-known Clos network. However,
`this cascaded architecture typically requires up
`to thousands of complex interconnects between
`switch submodules, thus decreasing serviceability
`of the overall switching system. In addition, the
`free-space beam propagation distances among
`port-to-port switching are not constant; there(cid:173)
`fore, insertion loss due to Guassian beam propa(cid:173)
`gation is not uniform for all ports. The minimum
`and maximum insertion losses of OMM's 2D 16
`x 16 switching subsystem has a difference of
`greater than 5 dB. 2D optical switches find appli(cid:173)
`cations in areas of communication networks,
`which requires smaller port sizes.
`
`30 MEMS SWITCHES
`
`A 30 or analog MEMS switch has mirrors that
`can rotate about two axes. Light can be redirect(cid:173)
`ed precisely in space to multiple angles -
`at
`least as many as the number of inputs. This
`approach results in only Nor 2N mirrors. Cur(cid:173)
`rently, a majority of commercial 30 MEMS
`switch designs use two sets of N (total of 2N)
`mirrors to minimize insertion loss. Alternatively,
`if only N mirrors were used, port count would be
`limited by insertion loss that results from finite
`acceptance angle of fibers/lens. Another advan(cid:173)
`tage is that differences in free-space propagation
`distances among ports-to-ports switching are
`much less dependent on the scaling of the port(cid:173)
`cou nt. This architecture can be scaled to thou(cid:173)
`sands by thousands of ports with high uniformity
`in losses. Inevitably, much more complex switch
`design and continuous analog control are need(cid:173)
`ed to improve stability and repeatability of the
`mirror angles. Lucent Technologies announced a
`30 optical crossconncct using MEMS mirror
`array called WaveStar'" LambdaRouter [2). The
`mirror can rotate on two axes and is continuous(cid:173)
`ly controllable to tilt greater than ±6°. Figure 4
`shows a closeup view of the WaveStar MEMS
`mirror.
`In the first quarter of 2001, Agere Systems,
`the former Microelectronics Group of Lucent
`Technologies, announced a fully integrated, 30
`64 x 64 MEMS optical switch component that
`will be marketed to makers of optical network(cid:173)
`ing systems. The 5200 series MEMS switch mod(cid:173)
`ule is based on the scalable 3D switching
`architecture developed at Lucent Technologies.
`Amazingly, the switching module has a maxi(cid:173)
`mum insertion loss of 6 dB and a switching time
`of less than 10 ms. Another notable develop(cid:173)
`ment in 3D MEMS optical switch is by Norte!
`Networks. Nortel made headlines at Optical
`Fiber Conference (OFC) 2000 by showing the
`first ever all-optical switch, called the X-1000, to
`beat the 1000-port barrier. Following the hype
`created at OFC 2000, Norte! has recently admit(cid:173)
`ted that only a small portion of the X-1000 actu(cid:173)
`ally worked. Nortel's 3D switching architecture is
`illustrated in Fig. 5.
`Nortcl's 30 switching architecture utilizes
`two sets of N mirrors for a total of 2N mirrors.
`The first plane of N mirrors redirect light from
`N input fibers to the second plane of N mirrors.
`All the mirrors on rhe second plane are address(cid:173)
`able by each mirror on the first plane making
`nonblocking connections. In turn, mirrors on the
`second plane can each be actively and precisely
`controlled to redirect light into desired output
`fibers with minimum insertion loss.
`
`ACTUATING MECHANISMS
`MEMS tilting mirrors alter the free-space propa(cid:173)
`gation of light beams by moving into their prop(cid:173)
`agation paths, thus achieving their switching
`functionality. In order for MEMS to be a viable
`optical switching technology, the actuating mech(cid:173)
`anisms used to move these mirrors must be
`small, easy to fabricate, accurate, predictable,
`reliable, and consume low power. This section
`briefly describes three actuating mechanisms
`
`160
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`LEEE CommuniClltions Magazine • November 2001
`
`

`

`that are being researched extensively in the uni(cid:173)
`versity laboratories as well as the industry.
`
`ELEcrROSTATIC
`Electrostatic forces involve the attraction forces
`of two oppositely charged plates. The advantages
`of electrostatic actuation arc that it has very well
`researched and understood behavior. Further(cid:173)
`more, it has very good repeatability, a property
`very important in optical switching. The disadvan(cid:173)
`tages include nonlinearity in force vs. voltage rela(cid:173)
`tionship, and requirement of high driving voltages
`to compensate for the low force potential.
`The design usually involves mirrors being
`held in parallel plane (OFF) to the underlying
`electrodes. When an electrode is charged at a
`different voltage level than that of its corre(cid:173)
`sponding mirror, the mirror will be tilted down
`to its ON position and thereby reflect a light
`beam to a different output fiber. Toshiyoshi and
`Fujita of the University of Tokyo demonstrated
`a 2 x 2 switching matrix using electrostatic actua(cid:173)
`tion. An optical switching matrix with large isola(cid:173)
`tion of 60 dB and small crosstalk of -60 dB and
`insertion loss of 7.66 dB are achieved using a
`bulk micromachined torsion mirror [31. Figure 6
`shows a 2 x 2 switching matrix with collimated
`light beams from input collimated beam fibers
`{CBFs) being reflected off torsion mirrors, fabri(cid:173)
`cated at 45• to light beams, into receiving CBFs.
`One of the leading MEMS optical switching
`companies, OMM, has already started shipping
`MEMS switching subsystems, based on electro(cid:173)
`static actuation, in production quantities since the
`spring of2000. 2D switching subsystems of sizes 4
`x 4, 8 x 8, and 16 x 16 arc hermetically sealed
`and passed Tcloordia Technologies' environmen(cid:173)
`tal and reliability requirements for carrier-class
`equipment. Passing of the stringent T elcordia
`tests, which include mechanical reliability and
`endurance, will help to facilitate widespread
`acceptance of MEMS-based switching subsystems
`in telecommunication networks. These switches
`have been used to route live data traffic in an
`unmanned central office in Oakland, California,
`with great success. OMM cites insertion loss of
`more than 6 dB, crosstalk of -50 dB, and switch(cid:173)
`ing time of 13 ms for a 16 x 16 subsystem.
`
`Torsion mirror chip
`
`t ·~
`
`• Figure 5. A schematic illustration of Noners 3D switching architecture.
`
`ELEcrROM AGNETIC
`
`Electromagnetic actuation involves attraction
`between electromagnets with different polarity.
`The advantages of electromagnetic actuation arc
`that it requires low driving voltages because it
`can generate large forces with high linearity.
`Disadvantages such as shielding from other mag(cid:173)
`netic devices to prevent crosstalk is difficult, and
`it has yet to prove reliable. The California Insti(cid:173)
`tute of Technology has developed a magnetic 2 x
`2 MEMS fiber optical bypass switch (4]. T he
`operation principle of the magnetic MEMS
`switch is illustrated in Fig. 7. The thin double(cid:173)
`sided bulk-micromachincd mirror moves up or
`down in response to changing magnetic field.
`When the mirror moves up, it blocks the optical
`path to opposing optical fibers. In this case, light
`signal is reflected off the mirror into neighboring
`optical fibers. When the mirror moves down, it
`moves below the level of the optical fibers, and
`light signal is transmitted to opposing optical
`fibers. Electromagnetic actuation can achieve
`this displacement with less than 100 mW.
`Integrated Micromachines Inc. ( IMMT),
`based in Monrovia, California, has developed a
`3D MEMS switching subsystem that has much
`lower loss than its competitors. It claims an
`
`• Figure 6. An overa/12 x 2 optical switching matrix design {3/.
`
`:.
`
`.• Counter electrode
`
`IEEE Communications Magazine • November 2001
`
`161
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`

`

`SDAs [7]. The translation movement of the
`translation plate by the SDAs is converted to a
`rotation movement of the mirror. Figure 8 shows
`the complete structural design of the FS-MOS.
`The length of the pushrod is 75 I!ID, and the dis(cid:173)
`tance between the hinges at the bottom of the
`mirror to hinge joint located on the mirror is 70
`l!m. This design allows the mirror to be rotated
`up to 45• when the translation plate is moved 2
`11m, and 90• at a translation distance of 22 11m.
`The number of bias pulses applied to the SDAs
`determines the plate translation distance, and
`thus the rotation angle.
`The optical switch has shown to have a
`switching time of 700 liS for rotating the mirror
`from an OFF position to the ON position. Loss(cid:173)
`es measured range from a minimum of 3.1 dB to
`a maximum of 3.9 dB. Jn this design, SDAs have
`been shown to have very fast responses and
`extremely precise translation movement. With
`the presence of the push rod and hinge joints, the
`mirror can be rotated to multiple angles precise(cid:173)
`ly and reliably, two of the most important
`requirements of 3D MEMS switches. As dis(cid:173)
`cussed earlier, the current 3D MEMS switches
`require the mirrors to be rotated about two axes.
`Novel designs incorporating SDAs to provide
`precise positioning of mirrors about two axes of
`rotation have the potential to reduce needs for
`complex feedback control electronics.
`
`CHALLENGES
`In the short term, MEMS appears to be the
`forerunner that has the potential to dominate
`applications including OXC~. OADMs, and ser(cid:173)
`vice restoration/protection switches. There
`remain important issues within MEMS technolo(cid:173)
`gy that need to be addressed before widespread
`acceptance in the core transport network.
`Re l iabili ty- Like any other commercially
`viable products, MEMS switches should function
`reliably in changing and often adverse environ(cid:173)
`ments. Will the behavior of MEMS switches that
`have been held in the ON position for a few
`months before switching to OFF during network
`restoration/provision be predictable? Or will stic(cid:173)
`tion between materials restrict the movements of
`the switches? Will switch response times and
`structural integrity of the optical switches
`degrade after millions upon millions of switching
`cycles? Concerns regarding reliability of MEMS(cid:173)
`based devices and repeatability in terms of per(cid:173)
`formance need to be well studied in the context
`of entire optical systems.
`Manufactu rability - Characteristics of
`MEMS-based devices could fluctuate from one
`batch to the next. Repeatability of material
`properties and uniformity of processing tech(cid:173)
`niques have to be improved to fully address
`these concerns. MEMS/CMOS fabrication pro(cid:173)
`cesses have to be made compatible. The control
`electronics and wiring schemes can be fabricated
`in sync with MEMS components, thereby elimi(cid:173)
`nating costly hybrid integrations. Researches
`into novel materials and fabricating processes
`must be ongoing. MEMS should be driven by
`technology as well as basic science.
`Serviceability- Matrices of micro-mirrors
`are fabricated using batch fabrication technique.
`
`• Figure 7. A schematic illustration of operation
`principle of the 2 x 2 bypass fibre optic switch [ 4 ).
`
`• Figure 8. A sche!7Ultic design of a free-rotating fiber optic switch {5].
`
`insertion loss of 3 dB regardless of ~witch size. By
`. using electromagnetic actuation instead of the
`weaker electrostatic actuation, lMMI claims that
`the driving voltage does not exceed a maximum
`of 10 V. Low power requirement is a critical crite(cid:173)
`rion especially when IMMI is looking to develop
`so-called 1000 x 1000-port monster switching sub·
`systems. Low insertion loss and low power con(cid:173)
`sumption bring benefits on both the system and
`economic levels. Now less optically efficient but
`more manageable fiber array connectors can be
`used, thereby reducing servicing time. In addition,
`MEMS/complementary metal oxide semiconduc(cid:173)
`tor (CMOS) integration, which eliminates tens of
`thousands of individual mirror control wires, is
`possible with lower voltage requirements.
`
`SCRATCH DRIVE ACTUATORS
`AT&T research labs have demonstrated an 8 x 8
`free-space micromachined optical switch (FS(cid:173)
`MOS) for the application of restoration and pro(cid:173)
`visioning in core transport lightwave networks
`[5]. The mirror and the scratch drive actuators
`(SDAs) are monolithically integrated on the sili(cid:173)
`con substrate using surface micromachining
`techniques. The rotation of the mirror is
`achieved by connecting the pushrods with the
`mirror and the translation plate using micro(cid:173)
`hinges [6). The actuators used are an array of
`
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`TEEE Communications Magazine • November 2001
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`

`

`When compared
`
`to their
`counterparts,
`MEMS optical
`switches are
`cheaper because
`of batch
`fabrication
`techniques.
`They are also
`
`smaller in size
`and lighter in
`mass thus
`allowing
`high-density
`packing on a
`single silicon
`substrate.
`
`Will the failure o f a single mirror require the
`replacement of the entire optical switch?
`Although t he inclusion of redundancy in the
`optical switches will a lleviate the problem, it
`remains to be fully explored.
`Scalability- The ability to incorporate more
`port counts when needed is the number one con(cid:173)
`cern of carriers. T he increasing amount of data
`traffic in communication networks, especially for
`long-distance carrie rs, will demand even more
`wavelengths to be deployed. Therefore, optical
`switches need the capability to scale in orde r to
`manipulate the increased number of wave(cid:173)
`lengths. MEMS-based optical switches must
`incorporate this key feature to gain widespread
`acceptance of the carriers.
`Standardization - There is a lack of techno(cid:173)
`logical compatibility in the MEMS optical switch
`market. It is shortsighted to rely on a single ven(cid:173)
`dor for MEMS-based optical switches. However,
`standardization will come with time. Simi larly,
`there should be compatibility in the front-end
`MEMS fabricating processes. Ultimately, the(cid:173)
`MEMS industry should mimic what the integrat(cid:173)
`ed circuit industry has done. Fabrication of a
`MEMS/application-specific integrated circuit
`(ASIC) can be contracted to cen tra lized
`foundries specializ ing in making MEMS devices.
`To achieve this, standardized fabrication pro(cid:173)
`cesses/libraries must be defined.
`Packaging- MEMS-based optical switches
`have close interaction with the physical world
`through their mechanical components. How will
`optical switches be packaged so as to minimize
`effects o f changing temperature, humidity, vibra(cid:173)
`tions, and other environmental e lements? Pack(cid:173)
`aging invariably affects the performance of
`MEMS devices. Therefore, it should be included
`in the initial design phase.
`Automation - Assembly of MEMS compo(cid:173)
`nents, and automatic optoelectronic packaging
`and performance testing of MEMS devices are
`crucial to reducing product cost and cycle time
`while maintaining product quality. Issues such as
`self-testing, self-assembly, and automated pack(cid:173)
`aging remains to be fully explored.
`Competing Technologies- MEMS-based opti(cid:173)
`cal switches a re facing major challenges from
`other all-optical switch technologies, and the con(cid:173)
`stantly evolving electronics switching systems. The
`current state-of-the-art electro nic switching sys(cid:173)
`tems offer 512 2.5 Gb/s ports for a combined
`capacity of over 1 Th/s. It seems that the adoption
`of optical switching technologies are faced with
`fierce resistance from electronic switching systems.
`It should be noted that Lucent's Lambda Router
`has yet to be commercially successful and is con(cid:173)
`stantly being outsold by electronic switching sys(cid:173)
`tems such as Ciena's CoreDirector. Given the
`current advancement of electronic switching tech(cid:173)
`nology, switching technologies such as MEMS will
`have a lot more to prove before we can e nter the
`era of purely optical switching networks.
`
`CONCLUSION
`MEMS optical switches have been demonstrated
`to have lower PDL, bit-rate- and protocol-inde(cid:173)
`pendent, lower insertion loss, and lower crosstalk
`than guided-wave solid state switches. Their supe-
`
`rior low loss performance a llows the m to be
`expandable to larger port counts. When com(cid:173)
`pared to their counterparts, MEMS optica l
`switches are cheaper because of batch fabrication
`techniques. They are a lso smaller in size and
`lighter in mass, thus allowing high-density packing
`o n a single silicon substrate. Curre ntly, the re is
`much research interest in integrating micro-optics
`and electronics components to MEMS devices to
`realize true integrated optics. Amidst aU the hope
`and hype, a MEMS-based optical switch has yet
`to cross major technological hurdles in order to
`fulfill its potential as the preferred optical switch(cid:173)
`ing technology in the long term.
`
`REFERENCES
`{1] K. E. Petersen. "Silicon As A Mechanical Material," Proc.
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`BIOGRAPHIES
`TZE-WEI YEOw (yeow@mic.utoronto.ca) obtained a B.A.Sc.
`degree in e lectrica l and computer engineering and an
`M.A.Sc. in mechanical and industrial eng ineering from the
`University of Toronto. Ontario, Canada, in 1997 and 1999,
`respectively. He is currently pursuing his Ph.D. degree in the
`Robotics and Automation, and Network Architecture Labora(cid:173)
`tories at t he University of Toronto. His research interests
`include developing novel MEMS devices for biomedica l
`imaging and switch architecture for optical crossconnects.
`
`K. L. EDDIE LAW (eddie@com m .utoronto .ca) received a
`B.Sc.(Eng.) degree in electrical and electronic engineering
`from the University of Hong Kong, an M.S. degree in electri(cid:173)
`cal engineering from Polytechnic University, Brooklyn, New
`York. and a Ph.D. degree in electrical and computer engineer(cid:173)
`ing from the University of Toronto in Canada. From 1995 to
`1999 he worked in three different groups-- Passport
`Research Group, Next Generation ATM Systems Department,
`an d Computing Technology Lab- in Norte! Networks,
`Ottawa. Since September 1999 he has been an assistant pro·
`lessor in the Communications Group in the Edward S. Rogers
`Sr. Department of Electrical and Computer Engineering at the
`University of Toronto. His current research interests are active
`networkings, policy-based management on the Intern et,
`TCP/IP protocol development, and photonic switch design.
`
`ANDREW A. GOLDENBERG IFI (go ld en@m ie.utoronto.ca)
`received B.A.Sc. and M.A.Sc. degrees from the Technion(cid:173)
`Israel Institute o f Technology, Haifa, Israel, in 1969 and
`1972, respectively, and a Ph.D. degree from the University
`of Toronto, Ontario, Canada, in 1976, all in electrical engi(cid:173)
`neering. From 1975 to 1981, he was employed by Spar
`Aerospace Ltd., Toronto, where he worked mainly on con(cid:173)
`trol. ana lysis, and d es ign of the space shu ttle remote
`manipulator system and satellite controls. Since 1987 he
`has been a professor of mechanical engineering at the Uni(cid:173)
`versity of Toronto. His current research interests are in the
`field of MEMS sensors-actuator-devices with applications in
`robotics and industrial automation. He is a former Editor
`of IEEE Transactions on Robotics and Automation . He is a
`member of the American Society of Mechan ical Engineers
`and the Professional Engineers of Ontario.
`
`IEEE Communicatio.ns Magazine • November 2001
`
`163
`
`